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FROM DEMOD 3N5 United States Patent 9 3 432 613 FACSIMILE TRAN SCE IVERSYSTEM WITH SUPERVISOR LOGIC CONTROL Waldemar Saeger, La Canada, RobertW; Reynolds, Les 1 Angelesy-Leland Dale Green, Sierra Madre, Armand R.Tanguay, Pasadena, and George T. Shimabuknro, Monterey Park, Calif,assignors toXerox Corporation, Rochester, NLY., a corporation of NewYork Filed Oct. 1, 1965, Ser. No. 492,203 U.S. "Cl. 178-6 11 Claims Int.Cl..H04n3/00, 7/00 This. invention relates to facsimile'equipment andmore particularly to facsimile transceivers adapted to operate throughthe direct distance dialing telephone network either with or withoutdirect electrical connection thereto.

Facsimile transmission is old in the art. In the past, it has mostlybeen used for transmitting photographic type of information overpredetermined leased transmission channels' More recently, equipment hasbeen marketed for the high speed transmission of documents over broadband-transmission channels. The present invention is particularlyconcerned with the economical and flexible transmission of letters,drawings and other black-white documents over ordinary voice gradetelephone channels.

The equipment meeting these goals should be inexpensive and theinvention accordingly, provides a facsimile transceiver wherein many ofthe components are shared between the transmitting and receivingfunction, instead of a separate transmitter-and receiver.

g It is desirable that the equipment becapable of transmitting documentsany location where telephones are available. The invention provides afacsimile transceiver which is capable of either transmitting orreceiving'documents through any conventional'telephone set without re- 1quiring an electrical connection thereto. The invention provides afacsimile transceiver capable of establishing 1 synchronism with a liketransceiverat a remote location independently of the character,frequency, or phase of the power line to which each. may be connected."

The equipment should minimize the telephone charges associated with thetransmission of the document. The invention provides equipment whichdoes not require the operator to lease a so-called data set from thetelephone company, which transmits documents in a shorter time than hasheretofore been possible, and which permits the equipment operators ateach .end of the transmission link toiterminate the telephone connectionas soon asthe connectionis norlonger actually needed or whenevertransmissionbecomes unintelligible.

The equipment should also becapable of operating 5 through telephonecompany data sets where available, to

take advantage of their improved transmission capability. The inventionprovides a facsimile transceiver which opcrates withtwolevel signalswhich will interface truth a conventional .data set intended for thetransmission of digital signals: through telephone lines. I

The equipment should function reliably w1thout regard to the skill ofthe operator. The invention provides a facsimile transceiver whichrequires only the insertion of a piece of paperand the dialing of atelephone call in order "ice FIGURE 4 is a simplified isometric view ofthe trans mitting mechanism.

FIGURE 5 illustrates logical circuit elements used in the subsequentfigures.

FIGURE 6 shows the basic timing circuit.

FIGURE 7 shows the repetitive waveforms corresponding to FIGURE 6. 7

FIGURE 8 shows the transmitter and telephone transducer controls.

FIGURE 9 shows the transmitter logical circuitry.

FIGURE 10 shows waveforms generated in the circuit of FIGURE 9.

FIGURE llshowsa video amplifier circuit used in FIGURES 9 and 10.

FIGURE 12 shows the printerpower and control circuits.

FIGURE 13 shows an alternate form of FIGURE 12.

FIGURE 14 shows'thestepping motor drive amplifier.

FIGURE 15 shows the printer logical circuits.

FIGURE 16 shows waveforms illustrating the achievementofsynchronization.

FIGURE 1 shows the external appearance of a form of facsimiletransceiver according to theinvention. The apparatus is enclosed by acabinet including a generally-horizontal aperture 121 'in its forwardlyfacing surface. Visible within the aperture is a rotatable drum 122including a clamp bar 123. Aperture 121 permits access to the drum sothat an operator may'fasten a sheet of paper to the drum to make afacsimile recording thereon. On top of the cabinet is a tray 124 forholding a document to be transmitted and feeding it through a slot 125into the scanner mechanism 126 Cabinet 120 also includes a reset buttonand an indicator light 131. Adjacent to the cabinet 120 andconnected'thereto is a box 127 which is adapted to contain astandard'telephone hand setand is provided with a hinged cover 128 andlatch 129.

FIGURE 2 is a schematic diagram showing, in general terms, how two ofthe facsimile transceivers of FIGURE 1, each at a different location,may be interconnected to form a bidirectional facsimile system. Itshould be understood'however, that 'the functional blocksshown in FIG-URE 2 correspond in onlya very general way to the circuitsoracircuitfunctionsdescribed in subsequent figures.

The first step in sending a document is for the operator at one locationto use his telephone to dial the correspondingtelephone l35 at theotherlocation, generally through one or more intervening telephone exchanges13 6; After a normal voice connection'has been confirmed by the operatorat each piece'of equipment, each operator places his handset 137 inbox-127 and closes the cover. Either operator inserts a document throughslot 125 into the scanner-126 of his unit. Scanner126 then sends acontrol signal to'transmit/receive circuit .140 which, re-' sponsive tothe'document in scanner 126 and the handset in box 127, adapts thetransceiver to the transmit mode. Scanner 126 also sends video signalsto transmitter 138 which processes the signals and uses'them tocontrol'the operation of scanner 126. Meanwhile, transmitter 138combined the video signals withcontrol signals from transmit/ receivecircuit 140 and introduces them into handset 137 from which they aretransmitted over the telephone line. At the same time, even thoughtransmitting is taking place, timing and power'circuit139 is exchangingsignals with printer 142 and generatingfurther signals for processing bytransmit/receive circuit 140.

At the other transceiver a signal is picked up from the. corespondinghandset 137 and detected by receiver.

141' which causes transmit/receive circuit 140' to putthe transceiverinto the receive mode. The received signals also cause transmit/receivecircuit 140 to control the operation of timing and power circuit 139 soas to bring printer 142 into synchronism with scanner 126 of thetransmitting transceiver. The received signals are applied to printer142 and cause it to record a facsimile of the transmitted document.

At each transceiver a supervisory circuit 143 monitors the operation ofthe various circuits so that a corresponding alarm sounds at each of thetwo transceivers when a transmission is either completed or interrupted.The alarm signals each of the two operators to lift up their handsetsand talk to each other to deter-mine whether documents are to beretransmitted, more documents are to be transmitted in either direction,or whether the telephone connection should be terminated.

It is obvious from the preceding description that an unlimited number offacsimile transceivers according to the invention may be used inconnection With each other, since any one can be functionally connectedwith any other, for either transmitting or receiving, through theconventional switching facilities of the telephone companies. Conferencecall arrangements may also be used to permit one transceiver tosimultaneously transmit to a number of others.

FIGURE 3 is a simplified isometric view of the printing or recordingmechanism. Drum 122 is journaled for rotation in bearings, not shown,and is driven through gears 151, 152 and 153 by motor 150 which ispreferably, although not necessarily a two pole synchronous motor withmeans, for example a permanent magnet rotor for providing a predictablerelationship between electrical power phase and rotational phase. Motor150 bears a pinion 151 which drives idler gear 152 at a 2 to 1 reductionratio, and idler gear 152 drives drum gear 153 at a to 1 reductionratio. Attached to drum 122 are a pair of cams 162 and 163 which actuateswitches 164 and 165 respectively. The functions of these switches willbe described subsequently in connection with a description of FIGURES 6and 12. A pen carriage 154 is located adjacent to drum 122 and slideablymounted on rails 155 which are parallel to each other and to drum 122.The pen carriage 154 carries a marking tip 156 which may be urged intocontact with the drum by an electromagnetic assembly 157 and urged awayfrom the drum by spring 158. A flexible electrical cable 166 carirescontrol voltages to the electromagnetic asembly 157 and to marking tip156 itself. The pen carriage 154 also engages a lead screw 159 which isincrementally driven by either a forward stepping motor 160 or reversestepping motor 161, the two stepping motors being connected to eachother, and to the lead screw. In this manner, marking tip 156 can beadvanced in. uniform discrete increments on the order of 0.01 inch in adirection parallel to the axis of the drum in response to commandsderived from circuitry which will be described later on.

Marking tip 156 may take many different forms as is known in the art. Itmay comprise an electrically insulated metal stylus adapted to writedirectly upon conventional electrolytic facsimile recording paper. Thesame form of stylus can be used to deposit electrostatic charge on aninsulating sheet for subsequent development by known xerographictechniques. A simple metal stylus can also be used to record directly onpressure sensitive recording paper through selective energization ofelectromagnetic assembly 157. Various forms of aparatus for theselective deposition of liquid ink may be employed. A variable intensityfocused light source may also be employed for forming a latent image ona sheet of photographic paper of the like. Any of these methods or anyother suitable facsimile recording techrnique may be employed with theinvention.

FIGURE 4 is a simplified isometric view of a form of scanning mechanism126. A pair of drive rolls 176 is provided with a cog wheels 177, as isa stepping motor 178 which may be identical with motor 160 or 161 ofFIGURE 3. Motor 178 incrementally drives rolls 176 through a so-calledtiming or cogged belt 179. Each drive roll 176 cooperates with a pinchroller 180 immediately above it to feed a sheet of paper through thescanner in increments on the order of 0.01 inch. Fluorescent lamps 181,preferably operated by direct current, are positioned beneath driverolls 176 and are provided with reflectors, not shown in this figure, todirect light upwardly against the lower surface of a sheet of paperpassing through the rolls, and supported on a slit-containing platen,also not shown in this figure. A mirror galvanometer 183, including asmall mirror, 184, samples light reflected from the sheet of paper andpasses it through lens to photomultiplier 186 or other photosensitivedevice. Since the mirror galvanometer is a device adapted torotationally oscillate the mirror about an axis, the photomultiplier 186is enabled to scan a sampling spot back and forth in a line across adocument or other sheet of paper passing through the drive rolls.

FIGURE 5 illustrates certain forms of elementary logic circuits whichare widely used in subsequent figures of this specification. FIGURE 5Ashows the NAND and NOR gate symbols and a suitable transistor circuitfor realizing the function represented by the symbols. The illustratedNAND and NOR symbols actually denote the same circuit function, asshown, for example, in MIL-STD-806B, Feb. 26, 1962. In terms of theillustrated transistor circuit, the symbols represent the followingfunction: the output voltage is minus 6 volts if, and only if, allinputs are at zero volts, otherwise the output is at zero volts. It isconvenient to regard most of the gates in later figures and NAND gateswith 1 equal to zero volts and 0 equal to minus 6 volts. FIGURE 5B showshow two of the circuits of FIGURE 5A can be cross-coupled to provide aflip-flop circuit. The flip-flop is characterized in that it will changestate only when an input voltage of minus 6 volts is applied to theappropriate input terminal. Specifically, if minus 6 volts is applied tothe Reset" input, then the fiip-fiop will be Set, i.e., the 1 outputwill be at zero volts and the 0 output will be at minus 6 volts. FIGURE5C shows an obvious and self-explanatory modification of FIGURE 5B inwhich the flip-flop can be set to one of its states by a voltage ofminus 6 volts applied to either of two corresponding inputs. FIGURE 5Dshows how an inverter function is provided by the logic gate of FIG. 5A.FIGURE 5B shows a trigger flip-flop which changes state as a result ofthe pulse applied to the single input terminal. In the form used in thisspecification, the input signal is a six volt positive going pulse andthe output voltages are either zero or minus 6 volts. The illustratedtransistor embodiments of the described circuit functions can beobtained in module form from the Engineered Electronics Company of SantaAna, Calif. The NAND/NOR circuit is their model Q-411 or Q-421 and thecircuit of 5B represents two model Q-412 or Q-422.

The symbols and circuits of FIGURE 5 represent those chosen for use inthe illustrative embodiment of the invention. The functions representedby the logic symbols can be realized by circuits of many formsobtainable from numerous manufacturers and all of which are well knownin the art. Those skilled in the art will also realize that logicalcircuitry of the type to be shown in subsequent figures has a certainoverall input-output relation which can be duplicated using differentarrangements of the same basic logical elements and furthermore, thatthis function can be realized using quite different types of logicelements which need not even be electronic. Merely as an illustration itmay be noted that AND/OR gates may be substituted forthe illustratedNAND/,NOR gates and that it might even be possible thereby to simplifythe described embodiment of the invention. In general, the designer willchoose the type and design of his logical building blocks based on suchconsiderations as cost, size, reliability, voltage and currentrequirements, speed, fan-in and fan-out capabilities, etc.

Timing circuits FIGURE 6 shows the timing circuits used to generate thetiming waveforms shown in FIGURE 7, which are used in controlling theoperation of the facsimile transceiver. A tuning fork or other stableoscillator 201 provides a 3840 cycle output frequency which is processedby pulse shaping circuit 202 to provide a train of posi tive-goingpulses at the oscillator frequency. These pulses are applied to acounter or divider chain of seven sequentially connected triggerflip-flops identified as I through VII. A higher frequency crystaloscillator with additional dividers may also be employed. Forconvenience the first six stages only are regarded as constituting adistinct scale of 64 counter 203 and are so shown in the figure. Eachcounter can be simultaneously reset to zero from a common source throughcoupling diodes 204, but the reset function will not be described exceptin connection with FIGURE 15. The output of stage VI is a 60-cyclesquare wave identified as signal A which is used to drive motor 150 asshown in FIG- URES 3, 12 and 13. The output of stage VII is a 30- cyclesquare wave I-I. Motor 150 rotates at 3600 r.p.m. and drives drum 122 at180 r.p.m. so that one revolution requires 333 milliseconds or 20 cyclesof signal A. Drum 122, acting through cams 162 and 163 and switches 164and 165 generates timing signals M, M and S in a manner which Will bemore fully shown in FIG- URE 12. In terms of the rotation of drum 122,signal M is in the zero volt or logical 1 state from 355.5 to 7.5 and Sis in the 1 state from 22 to 36. Signal M is simply the inverse ofsignal M. For reasons which will become apparent later, the otherwisearbitrary zero de gree position of drum 122 should be chosen at a pointwhere marking tip 156 is over clamp bar 123. Because of the fixedrelationship existing between frequency divider 203 and drum 122 it isconvenient to use the angular position of drum 122 for specifying thevarious waveforms generated in FIGURE 6. For convenience it may be notedthat in the illustrated embodiment one cycle of oscillator 201corresponds to .26 millisecond and also corresponds to 28 of rotation ofdrum 122. Thus, one degree of rotation corresponds to about .93millisecond.

The 0 outputs of stages III and IV of counter 203 are combined in NANDgate 205, the output of which is inverted by inverter 210, delayedslightly by capacitor 224 grid applied to AND gate 215. This signal isin the logical 1 state whenever counter 203 is at counts 0 to 3, 16 to19, 32 to 35, or 48 to 51. Further processing of this signal will bedescribed later.

The O outputs of stages V and VI of the counter are combined in AND gate206 and the resulting signal inverted to provide signal D which is inthe logical 1 state whenever divider 203 registers counts zero throughfifteen, inclusive. This output, accordingly, appears 20 times perrevolution at 0 to 4.5"; 18 to 225; 36 to 40.5 etc. and is referred toas the advance clock signal.

The 0 output of stage V is combined with the l output of stage VI ingate 207, the output of which is inverted in inverter 212 to provide asignal which is at the logical 1 level during counts 32 to 47 inclusive.This signal is combined in NAND gate 217 with incoming signal S which isat the 1 level from 22 to 36. The output of gate 217, inverted byinverter 228, is a signal which is at the logical 1 level from 27 to 315only and is identified as the prevideo signal G.

The 1 outputs of stages V and VI are cornbined in 49.5 etc. This signalis also inverted in inverter 213 toprovide a signal which is at thelogical 1 level from 13.5 to 18; 31.5 to 36 etc. and is used internallyas an input to gates 218, 220, 221, 222 and 223. The other input to gate218 is the 1 input of stage IV. Accordingly, the output of gate 218 isthe triple coincidence of counter stages IV, V, VI. This is inverted ininverter 229 to provide a signal which is at the logical 1 level forcounts 50 to 63 inclusive or 15% to 18; 33% to 36; 51% to 54, etc.

The triple coincidence of the 1 output of stages IV V, VI is alsodetected in gate 209, inverted in inverter 214, combined in gate 219with the 1 outputs of stages II and III and finally, inverted ininverter 230. The resulting signal is accordingly at the logical 1 levelfor counts 62 through 63 inclusive. This signal is identified as L andappears from 359.4 to 360; l7.6 18; 35.6 to 36 etc.

The output of inverter 213 is also combined in gate 220 with signal S toproduce a minus 6 volt output pulse extending from 31.5 to 36. Thispulse is applied to one input of flip-flop 231. The output of inverter213 is also combined in gate 221 with signal M to produce a minus 6 voltsignal extending from 355.5 to 0". This pulse is applied to the otherinput of flip-flop 231. Inasmuch as the flip-flop is alternately set andreset by the signals appearing at its two input terminals, a signal atthe appropriate output terminal will be at the logical one level from315 to 355.5. This signal is designated as video gate signal I. Theoutput of gate 221 is also inverted in inverter 132 to form a signalwhich is at the logical 1 level from 355.5 to 0 and which is referred toas video end signal E.

The output of inverter 213 is also applied to the first inputs of NANDgates 222 and 223, the outputs of which are connected to opposite inputterminals of a flip-flop 2 33. The second input of gate 222 is connectedto the signal M while the second input of gate 223 is connected to theinverse of signal M, namely M. Thus, flipfiop 233 changes state everytime signal M changes state, but the change is delayed in each instanceuntil a logical 1 signal is received from inverter 213. Accordingly,flip-flop 233 changes state at 355.5 and 13.5, rather than at 352.5 and7.5". The output of flip-flop 233, extending from 355.5 to 13.5 isdesignated signal N.

Returning to the previously described signal D, this signal is combinedin gate 216 with signal M which acts as a window to permit only one Dsignal per revolution to pass through. The resulting signal is invertedby inverter 227 and constitutes a signal B, which is at the logical 1level from 0 to 4-.5 only. The output of gate 216 is also applied to adelay multivibrator circuit 225 which delays it for nearly a fullrevolution of drum 122 to provide the signal Q shown in FIGURE 7.

Signal B is also combined in gate 215 with the previously describedoutput of inverter 210. The negative output of gate 215 thus extendsonly from counts 0 to 3 of counter 203 and only at the zero degreeposition of drum 122. The resulting signal is inverted in inverter 226to produce a signal designated C which is at the logical 1 level from 0to 1.13 only.

FIGURE 7 shows the above-described waveforms plus a synthesized waveformW which is the coincidence of the previously described F signal and theinverse of the described D signal. This composite signal extends from 45to 135; 225 to 315 etc. This particular waveform will be used inconnection with FIGURE 9 together with certain other illustratedwaveforms.

Transmitting circuits FIGURE 8 shows the scanner and telephoneassemblies schematically in somewhat greater detail, together with theirassociated circuitry. It can be seen that the fluorescent lamps 181,shown previously in FIGURE 4, are provided with reflectors 301 and thata platen 302 is provided to support a document face down as it passesthrough the drive and pinch rolls 176 and 180. A slit 303 is provided inthe platen between the lamps and immediately over the mirrorgalvanometer 183. Also shown in this figure is an aperture or stop 304which is positioned between lens 185 and photomultiplier 186 to limitand define the size of the sampling area which is scanned back and forthacross the document by mirror galvanometer 183.

Mirror galvanometer 183 may be suitable device capable of rapidlyconverting an input signal into a corresponding rotation of a mirror.Commercially available mirror galvanometers of the type sold for use inmultichannel optical recording oscillographs represent a suitable deviceof this type. A particularly suitable device for use in the illustratedembodiment of the invention can also be made by cementing a one-halfinch diameter mirror to the pen shaft of a pen recording galvanometer,catalog No. 428647-920138, manufactured by The Brush InstrumentsDivision of the Clevite Corporation, or to the shaft of comparabledevices made by the Sanborn division of Hewlett-Packard Company.

. Also shown in this figure are paper detector switches 306 and 307which are positioned to detect the presence of a sheet of paper in thescanner. Switch 306 detects the presence of a sheet of paper as it isfirst presented to the scanner on the left side thereof, and switch 307detects the presence of a sheet of paper within the scanner andapproximately at the position of slit 303. Switch 306 operates anassociated multicontact relay K1. and switch 307 operates an associatedmulticontact relay K2. Switch 307 may be replaced by a time delaycircuit actuated by switch 306. Operating power for these relays passesthrough a switch 308 which is located in telephone box 127, and which ispositioned so that it will close and pass current to relays K1 and K2only if a telephone handset is properly seated in the box. Only ifswitch 308 is properly closed will insertion of a piece of paper intothe scanner enable switch 305 to operate relay K1. Among its otherfunctions, relay K1 transfers a contact Klu which supplies minus 6 voltsto a resistor 312, the other end of which is grounded. The voltageappearing across resistor 312 is supplied to inverter 313, the output ofwhich is a transmitter control voltage T which is at the logical 1 levelonly when relay K1 is operated. This output T is used to control theoperation of the transceiver in the transmit mode. When switch 308 isclosed but relay K1 is not energized, minus 6 volts is appliedtoresistor 322 instead of resistor 312. The voltage appearing acrossresistor 322 is supplied to inverter 323, the output of which is at thelogical 1 level only when switch 308 is closed and relay K1 is notenergized and, therefore, provides a receiver control voltage R tocontrol the operation of the transceiver in the receive mode.

Relay K2 has a contact a which holds relay K1 closed as long as relay K2is closed. Accordingly, relay K1 will remain closed as long as adocument is still over slit 303 and signal T will remain at the logical1 level for that time. Relays K1 and K2 and other relays to be describedlater are shown with their contacts in the de-eneriized state of therelay. The relay contacts are not necessarily shown in physicalproximity to the relay coil symbol.

Drive motor 178 is shown in association with a pair of drive coils 305.Many types of stepping motors may be used for motor 178, or motors 160and 161. They may be, for example, an ordinary electrical solenoidassociated with a pawl and ratchet drive, a rotary solenoid associatedwith a one-way drive clutch, a driving mechanism of a conventionalstepping relay, or the so-called Cyclonome stepping motor sold by SigmaInstruments, Inc. This latter type is preferred and, as is Well known,incorporates a pair of driving coils, corresponding to referencecharacter 305, which are energized alternately by means to be shown inFIGURE 14.

Photomultiplier 186 is connected to a gated squaring amplifier 321, morefully illustrated in FIGURE 11.

The energization of galvanometer 183 is controlled by a contact 11 ofrelay K2 so that the galvanometcr is enabled to operate whenever adocument is in position above the slit 303. The galvanomcter drive powercomes from either a prescan generator 310 or a scan generator 320, underthe control of relay K6, which is under the control of the circuits ofFIGURE 9. Scan generator 320 provides a linear ramp voltage which issynchronized with the rotation of drum 122 by means of incoming signal 7from FIG. 6. Prescan generator 319 filters and amplifies the incoming30-cycle square wave H from FIG. 6 to provide a 30-cycle sine wavesignal which has ten cycles or twenty half-cycles per revolution of drum122. A triangular wave would also be suitable. Suitable circuits forgenerators 319 and 320 are to be found in FIG- URES 7 and 8,respectively, of S.N. 471,799, filed July 14, 1965. The reasons forproviding both a high speed and a low speed scanning waveform willbecome apparent later in the specification and are also set forth insaid S.N. 471,739, filed July 14, 1965.

Referring to telephone box 127, there is provided a small loudspeaker309 and a soft annular gasket 310 to seal the loudspeaker 309 to themicrophone unit of handset 137. Loudspeaker 30 9 is connected through arelay K4 to modulator 314. Relay K4 is operated by switch 308 so as toconnect the modulator to the loudspeaker only when the transceiver is inthe transmitting mode. The modulator may be of any of the varietiesknown to the art. A highly satisfactory form of modulator comprises avoltage controlled multivibrator oscillator followed by an audioamplifier, such that sound at 1300 cycles is applied to the telephonefor one of the levels of a two-level input signal applied to themodulator, and sound of about 2300 cycles for the other input level.This arrangement has proven very satisfactory for introducing facsimilesignals into a telephone circuit without making an electrical connectionthereto. When the transceiver is not in the transmit mode, loudspeaker309 is disconnected from modulator 314 and is connected through relay K4to an alarm tone generator 315 which is controlled from the alarmcircuits of FIGURE 13 and supplies a lower frequency sound, i.e., 800cycles, into the telephone.

An inductive pickup coil 311 is provided in telephone box 127 under theearphone end of handset 137 to pick up incoming signals. The coil may beof the shape shown and may be comprised, for example of 7900 turns of#34 insulated wire with an inductance of about 2.2 henries at 1000cycles. It has been found that there is sufficient leakage flux from atelephone receiver, particularly those used in the Western Electric 500subscriber set, to permit efficient signal pickup by means of theillustrated coil. As an alternative, particularly where the facsimileequipment must be used with other types of telephone instruments havingwell shielded receivers, pickup coil 311 may be replaced by a microphoneacoustically coupled to handset 137 for picking up the acoustic signalsradiated by the handset. The signals from coil 311, or from themicrophone, are demodulated in a demodulator 316 of a type appropriatefor use with the selected form of modulator 314 to produce an outputsignal corresponding to the input signal to modulator 314. If desired,coil 311 can also be used to couple signals into a telephone fortransmission. A terminal 317 is also provided on the output side ofdemodulator 316 to permit the direct reception of facsimile signals froma telephone company data set or the like, as an alternative to signaltransmission via a conventional telephone subscriber set, as shown inFIG- URE 8. A very sharply tuned, narrow band demodulator 313 is alsoconnected to pickup coil 311 to provide an output signal responsive todetection of a selected tone transmitted by alarm tone generator 315.

Voice grade telephone lines are a convenient facsimile transmissionmedium because of their universal availability, but provide a far fromideal transmission medium for facsimile or other data type signals. Forthis reason, it is desirable in modulator 3:14 and demodulator 316 toprovide the technical refinements which are known to the art, in orderto maximize the quality of transmitted images and the speed at whichthey can be transmitted.

While not a part of this invention, it has ,been found quency versusinput signal characteristics. At demodulator '316,- it is desirable toemploy delay equalization to compensate for the non-uniform delay versusfrequency characteristics of a typical telephone channel, and .to"apply-the resulting phase delay compensated signal to a wide bandfrequency modulation or frequency shift detector to derive a suitableoutput signal. Withthese refinements it is possible to achieve highquality facsimile transmission, making effective use of thenationalswitched telephone network, even allowing for the inevitable signaldegradation involved intransducin-g'the facsimile output signal througha loudspeaker into the carbon microphone of a telephone and intransducing the input signal from animperfect telephone receiver. Otherforms of modulation, such as amplitude modulation or vestigial sidebandmodulation may-also be employed.

FIGURE 9 shows the logical circuitry which is used to control theoperation of .theiacsimile scanner and to generate an-appropriatefacsimile signal for transmission. As

an aid in understanding the operation of. the illustrated circuits, thepaths of the principal transmitted signals, as opposed to internalcontrol signals, are shown in bold lines. There are four of thesesignals which are combined .in a four. input NOR gatetconsisting ofgates. ,402 and .-.405, gated against the transmit control signal ingate-406, and applied to the modulator 31 4, previouslydescribed inconnection with FIGURE 8. A terminal 422 is.also provided to permitthese signals to be applied directly to a data set. The first of thesesignals is the facsimile video signal itself, which is a two-levelsignal derived by amplifier 321 from. the output of photomultiplier .186which is, inturn, related point by point tothe density of a documentbeing scanned with the aid ofrmirror galvanometer 183. This signal isgated in NAND gates401 and 403.

One of these gating signals is the signal J which prevents the videosignal from ever gettingthrough to NOR gate 402 in the interval from-355.5 to 315 of the drum rotation of drum 3122, this period being allottedto the scanning of clamp bar 123- and for the. transmission of certaincontrol signals. The next signal of significance is the previouslydescribed once per revolution prevideo signal G which is gated in NANDgate.41 6 by an output of advance control vfiip flop .414. The. thirdsignal isthe 20 times per revolution advance clock signal D which isgated on and off in NAND gate 418 by the other output of flip-flop 414from that used to control the prevideo signal in gate 416. The fourthsignal E which is a one time per revolution signaland the inverse of thepreviously described B signal. This signal, unlike the others, isapplied directly to the NOR gates 419 and 405 without inversionin aprior NAND gate, .Thissigual rnust pass through a normally open ,contactof relay Klglld a normally closed contact of relay K2.

In addition to generating a composite video signal for transmission, thecircuit OfiFI GU-RIE ,9 generates two other important signals for.internal use one fyth se Signals is a composite of the D and I3 signalsonly, from the transmittedyideo signal. This signal is generated, by

means of a NAND gate419 which has the same input connections as NANDgate 405, andthe outputof which is gated in ,NAND gate 420 by thetransmit control signal, in the same manner as the composite videosignal is gated by gate 406. This signal is applied, through circuitsshown in FIGURE 12, to the scanner stepping motor 178, shown inFIGURE 8.Later, it will be shown that this component ofthe transmitted videosignal causes pen carriage .154 at a remoteconnected transceiver toadvance 10 incremently in synchronism with the document advance in-thetransmitting transceiver. The other signal produced in FIGURE 9 is theoutput of scan controlflip-flop 4 10 which is applied to relay K6 inFIGURE 8 to control .the operation of mirror galvanometer 183 betweenthe slow, one-l near scan per revolution mode, and the fast This samesignal is alsotransmitt'ed through'gates 419 and 420 to the apparatus ofFIGURE l2'from which it returns to stepplng motor 178 of FIGURES tooperate the motor at a rate-f l incremental advance per revolution ofdrum 122, ie three advances per second. The

transmitted signal under the described conditions is shown in FIGURE10a. When a document has advanced to the position of switch 307,. relayK2 will be energized thus opening normally closed contact K andinterrupting the transmission of the B signals. At the same time,contact K212 (FIGURE 8) will close and commence the scanning operationof mirror galvanometer 183. l 7

At this point, it is necessary'to' consider the signals emanating fromphotomultiplier amplifier 321 as well as v the initial states of controlflip-flops 408, 410, 414 and 417.

Assuming that the apparatus is to be adapted for use with ordinarydocuments having black on white information rather than the reverse,"the. output of amplifier321 Will'be: at the logical 1 level, i.e., zerovolts, when the photomultiplier is looking at a black element of thedocument and at the logical 0 level, i.e., minus 6 volts, when thephotomultiplier is looking at a white background element. Initially,i.e., before photomultiplier 186 sees any printed material or the like,flip-flops 408, 410, 414 and 417 will be in the 1, 0, 1, and'l states,respectively. This can'be verified by examining a subsequentdiscussionofthe operatlon of the circuit when photomultiplier 186 scanscompletely blank lines on the document after having scanned linescontaining marks,'printi'ng or the like. Under the mural conditions,flip-flop 410 acting through gate"404 prevents any signals fromamplifier 321 from being transmitted and also leaves relay K6 in FIGURE8 de-energlzed so that galvanometer 183 is connected to prescangenerator 319. Flip-flop 414 enables 'D' signals to pass through gate418 'and'to be transmitted through gates 405 and 406. This same signalis also transmittedthrough gates 419 and 420 to operate stepping motor173th FIG URE 8. Finally, fiipfiop 414 also disables g'ate'416 andprevents prevideo signal G from being transmittedi'The transmittedsignal under the described condition is shown 1n FIGURE 1%. Under' theseconditions, the transmitted document is advanced at the rate ofincrements'per second, which is 20 times as fast as lines can berecor'ded on drum .122. 'As will be shown later, pencarriage'154 isadvanced at this same rapid rate ina remotely connected matchingtransceiver.

As soon as a black area is detected in the document being scanned, theoperation of the circuit 01 FIGURE 9 ,becomes quite different. Theabsence or reductionof light falling on photomutiplier 186 causesalogical 1 output ,signal. to be. produced by squaring amplifier. 321'and' this signal is enabled to pass through gate 403 to set flip-flop408 to the 0.state.v and thereby reset flip-flop 410 to the 1 statel'Thenew state of flip-flop 410 'causesgalvanometer 103 to be connected totheslow scan generator. 320 rather than. thefastprescan generator; Atthe next coincidence of the F and F signals (see FIGURE 7) the logical 1level at the Ooutput of flip-'flop408 is enabled to pass through gate411 to .set flip-flop 414 to the 0 state, thereby 75.

preventing any further advance clock signals D from passing through gate418, but permitting the next D signal to set flip-flop 408 to the 1state through gate 407. No further signals are transmitted until thenext appearance of prevideo signal G. The transmitted signals during adrum revolution of this type are shown in FIGURE 10c. At the nextappearance of the prevideo signal G the level at the output of flip-flop414 is enabled to pass through gate 416 to set flip-flop 417 to the 0condition at the same time the G signal is applied to NOR gate 402 andpasses through gate 406 for transmission. The 0 output of flipfiop 417is applied to gate 404 and directly thereafter (see FIGURE 7) video gatesignal I is applied to gate 401. The combined presence at gates 401 and404 of signal I. the 0 output of flip-flop 417, and the 1 output offlip-flop 410 enables the video signals from amplifier 321 to passthrough gate 401 and 404 and through gate 406 for transmission. Theremainder of this revolution, or slow scan cycle, is given over to thetransmission of video information detected by photomultiplier 186, asshown in F1"- URE d. It should be noted that the line now being scannedby galvaometer 183 is the same line which was scanned once before at amore rapid rate under control of prescan generator 319, since theinitial and immediate effect of the detection of a black area in thetransmitted document was to prevent any further advance clock pulses Dfrom either being transmitted to a remote transceiver or from beingapplied to stepping motor 178.

At the end of a slow scan of the type shown in FIG- URE 10d, the videoend signal E passes through gate 415 and sets flip-flop 414 to the 1condition, whereby the next advance clock signal D is enabled to passthrough gate 418. At the same time, 6 sets flip-flop 417 to the 1 stateand short master signal C is enabled to pass through gate 409 to resetflip-flop 410 to the 0 state and once again enable video signals fromsquaring amplifier 321 to reach flip-flop 408. Galvanometer 183 is nowagain connected to prescan generator 319 which is phased with respect tothe slow scan generator 320 so as to provide a rapid .retrace followingthe slow scan..If no black areas are detected in the document beingtransmitted during this retrace interval, the galvanometer will continueto be driven by the fast prescan generator 319 and advance clock signalD will be transmitted through gate 418 after each fast scan. Thetransmitted waveform will then be as shown in FIGURE 10d. However, assoon as a black area is detected, the circuit of FIGURE 9 will revert tothe slow scan mode already described and the transmitted signal for theremainder of the slow scan cycle will be as in FIGURE 10c. If a blackarea is detected along the very next scan line the transmitted waveformwill be as in FIGURE 10c.

The operation of the facsimile transceiver in the transmit mode can nowbe described in a simpler way. In the absence of black areas or othermarks which the photomultiplier and amplifier are designed to detect, adocument will be rapidly scanned alternately from left to right and fromright to left. No viedo information will be transmitted in thiscondition but characteristic advance signals will be transmitted andwill also be directed to the transmitter stepping motor to advance adocument one increment at the end of each scan. If a black area isdetected during a fast scan, then the document is not advanced anyfurther, a document advance signal is not transmitted, and the scanningaction reverts to the slow mode. When the scanning mechanism, i.e.,galvanometer 183, reaches the time and position at which a slow scan isabout to commence, a characteristic prevideo alerting signal istransmitted and thereafter video signals corresponding to the scan aretransmitted. At the end of the slow scan the document is advanced oneincrement, a paper advance signal is transmitted, and the galvanometerexecutes a rapid retrace during which video signals are not transmitted.If information is detected during the retrace, then a further slow scanis made and further paper advances or advance signals are withheld untilthe end of the slow scan. If no information is detected during the fastscan retrace, then the document is advanced at the end of the retrace,an advanced signal is transmitted, and further rapidseans and advancesare made until such time as black areas or other information aredetected. In this way, every elemental line of the document whichcontains information is scanned twice, first with a rapid scan and thenwith a slow scan during which video signals are transmitted. Linesbearing no information are merely scanned rapidly once. In this way adocument can be scanned many times more rapidly than as usual where allareas of the document are scanned at normal speed compatible with thetransmission medium being employed, i.e., a telephone circuit. It willbe appreciated that when scanning printer matter and particularlytypewritten letters and the like, the majority of the scan lines willtraverse only blank paper.

In a typical facsimile transceiver corresponding to the illustratedembodiment, the vertical resolution will be on the order of scan linesper inch and the horizontal resolution, along the scan lines, will beapproximately the same. This level of resolution is generally acceptedas being adequate for transmitting printing, typing, handwriting,drawings and the like without loss of information and with anaesthetically acceptable level of quality. Increasing the resolutionincreases the quality of reproduced images but also increases the timerequired to transmit a document. It has been found, on the other hand,that skipping alternate scan lines, while maintaining horizontalresolution unaltered, halves the time required to transmit a documentand provides intelligible, if less pleasing, facsimile copies where theoriginal subject matter is in the nature of printing or typing. Meansare provided to accomplish this result solely at the discretion of thetransmitter operator by including switch 421, gate 412 and inverter 413.With switch 421 open the circuit of FIGURE 9 operates as previouslydescribed. In particular, at the end of a slow scan flip-flop 414 is setto permit a single advance clock pulse D at the 0 degree position to betransmitted and to actuate stepping motor 178. Immediately after thispulse has been transmitted the If? signal passes through gate 411,resets flip-flop 414, and prevents the next D signal from passingthrough gate 418. With switch 421 closed, however, inverter 413 isconnected with gate 411 and the two together function as a four inputNAND gate. Now, the 30-cycle square wave, signal H, is inverted in gate412 and applied to inverter 41.3 and prevents the reset signal frombeing applied to flip-flop 414 during the critical period from 18 to 36of rotation of drum 122. This is the period in which the second D pulseappears. Accordingly, in this mode of operation two consecutive advancepulses are transmitted and also applied to stepping motor 178 beforeprevideo signal G is transmitted. A typical transmitted waveform in thismode of operation is shown in FIGURE 10 Thus, a document receives twoincremental advances between each slow scan.

The double skipping feature is valuable as described but may causenarrow horizontal lines or the like to be completely missed when thetransmitter is operating in this double skipping mode. The reference tonarrow horizontal lines is intended to cover those markings which wouldbe detected along only a single scan line. With the transceiveroperating in the fast skipping mode as shown in FIGURE 10]), detectionof information will cause the flip-flop 414 to be reset almostimmediately and prevent further transmission of advance clock signals D,as shown in FIGURE 100. With switch 421 closed, however, there wouldordinarily be a 50% probability that the signal 'fi would be at thewrong level and thus delay the resetting of flip-flop 414 and permittingthe transmission of one additional advance clock signal D. The ensuingslow scan would therefore not be of the line in which the informationwas detected but instead the next subsequent line.

This situation is substantially prevented by connecting the signal I tothe other terminal of gate 412, which is conveniently considered as aNOR gate. When double skipping from one black containing line to anotherthe circuit works exactly as previously described, fl being at the voltlevel in the relevant time interval. However, when information is firstdetected within a sequence of fast scans, T will be at the minus 6 voltlevel, and W will be enabled to reset advance control flip-flop 414regardless of the state of signal H, thus preventing the transmission offurther advance signals D.

FIGURE 11 is a simplified schematic diagram of the photomultiplieramplifier 321. An inverting voltage amplifier 501 amplifies thephotomultiplier output and provides a signal which is more positive whenthe photomultiplier looks at a white or background area and morenegative when it looks at a black area. This output signal is coupled toground through capacitor 502 and rectifier 503 which together functionas a peak rectifier providing an output voltage clamped to zero volts inbackground areas and negative in black areas. This voltage is coupled byresistors 505 and 506 to the normally positively biased base of pnptransistor 507. When the photomultiplier looks at a black area amplifier501 will produce a negative output signal which, will cause transistor507 to conduct and develop a 0 output from limiting post-amplifier 508.At other times the output of amplifier 508 is limited to minus 6 volts.During the time that photomultiplier 136 would otherwise be looking atthe edges of a document or other portions which are not transmitted,transistor 504 is gated off by a signal I as a result of which capacitor502 is not further charged but holds its charge in accordance with thetime constant determined by its value and that of resistors 505 and 506,i.e., re-

members the background level. Accordingly, the output from amplifier 321is a signal which is reliably at the preselected logical 1 value whenblack is being scanned and logical 0* when white is being scanned. Itwill be realized that more complex black/ white decision makingcircuitry may also be employed such as that disclosed in copendingapplications Ser. No. 329,640, filed Dec. 11, 1963, or Ser. -No.461,693, filed June 7, 1965.

Receiver and alarm circuits FIGURE 12 shows the power and controlcircuits of the printer portion of the transceiver. Recording drum 122is driven by a motor 150 as already shown in FIG- URE 3. Motor 150 isoperated by signal A from FIG- URE 6, after suitable amplification by apower amplifier 601. Pen carriage 154 is mounted on a lead screw 159driven by stepping motors 160 and 161 as also shown in FIGURE 3. In thisfigure, the individual drive coils 606 for motor 160 and 607 for motor161 are shown. The stepping motors used to incrementally drive leadscrew 159 may be of any suitable type as disclosed in connection withstepping motor 178; In the described embodiment stepping motor 160 and161 may be of the Cyclonome type manufactured by Sigma Instruments, aspreviously described in connection with stepping motor 178. A unitaryassembly of two of these uni-directional stepping motors mountedback-to-back on a common shaft is available under the designation model9AH. The stepping motors are driven by pulses applied in alternation tothe two drive coils and a special amplifier 608,

shown in greater detail in FIGURE 14, is provided to generate lthenecessary drive pulses. The output of this amplifier is connected tocontacts b and c of relay K1 (FIGURE 8) which direct the pulses toeither the recorder stepping motors of FIGURE 12 or the transmitterstepping motor of FIGURE 8. When a document is not being transmittedrelay K1 will not be energized and the contacts will be in theillustrated position wherein amplifier 608 is connected to the printingcomponents rather than the transmitting components.

A further set of relay contacts KM and K3e determine whether the pulsesare applied to forward stepping motor or reverse stepping motor 161.Relay K3 is illustrated in this figure and will be described. Tocomplete the description of this portion of the figure, it is noted thata further contact on relay K3 enables amplifier 608 to be driven eitherby the D pulses from FIGURE 6 or by pulses from a NOR gate 609 which isconnected both to gate 420 of FIGURE 9 and to gates 734 and 735 ofFIGURE 15, yet to be described. The pulses derived from FIGURE 9 areintended to be applied to stepping motor 178 of FIGURE 8 and this isaccomplished through previously described relay contacts K112 and K1cwhich switch the output of amplifier 608. The pulses from the circuit ofFIGURE 15 are the pulses intended to operate stepping motor 160 and willpass from amplifier 608 to motor 160 through the previously describedrelay contacts when a document is not being transmitted.

A power amplifier 610 amplifies the printing or video signal from FIGURE15 and applies it to the marking tip 156 and an amplifier 611 amplifiesthe pen engage signal from FIGURE 15 and applies it to theelectromagnetic assembly 157 of pen carriage 154.

Cams 162 and 163 are associated with drum 122 as previously shown inFIGURE 3. A voltage of minus 6 volts is applied through switch 164 togrounded resistor 602, and through switch 165 to grounded resistor 604,the switches being actuated by cams 162 and 163 respectively. Thevoltage appearing directly across resistor 602 is the previouslydescribed control voltage Id and this voltage when inverted in inverter603 is control voltage M. Similarly, the voltage across resistor 604 isinverted in inverter 605 and becomes control voltage 5. These voltagesare used to control the timing circuits of FIG- URE 6 and theirfunctions have already been described. It will be understood that thereare many other ways of deriving such control voltages from the rotationof drum 122. Magnetic proximity switches, photoelectric, detectors andthe like could be used equally as well as the illustrated cam operatedswitches. Furthermore, a switch or the like may be used to initiate acontrol signal at a desired position of drum 122 and a multiyibratorcircuit or the like may then be used to determine the duration of thesignal. It will also be understood that the functions of switches 164and 165 may be performed through the use of additional dividing stagesgating circuits and the like in FIGURE 6. However, the illustratedmethod of deriving these signals is particularly simple, economical, andreliable.

Limit switches 612 and 613 are positioned adjacent the ends of leadscrew 159 and are adapted to be engaged by pen carriage 154 at the leftand right limits of travel. Switch 613 has a normally open contact whichis closed by contact with the pen carriage at the end of the normaltravel of carriage 154 and switch 612 has a normally closed contactwhich is opened by the pen carriage as it returns to the startingposition. The closing of switch 613 energizes relay K3 which causescontact a to close and maintain relay K3 energized through a circuitincluding switch 612. The energization of relay K3 causes the input ofdrive amplifier 608 to be connected to D signals from FIGURE 6 andcauses the output of the driver amplifier to be transferred from forwardstepping motor 160 to reverse stepping motor 161. A further contact onrelay K3 causes a control voltage to be sent to the circuit of FIGURE15, yet to be described. With relay K3 energized, pen carriage 154 isreturned rapidly to the left at the rate of 60 increments per second bystepping motor 161. When carriage 154 returns to the starting position,it opens switch 612 which deenergizes relay K3 and returns the variousstepping motor drive connections to their normal forward position,preparatory to recording a new document on drum 122.

1. AN IMAGE SIGNAL TRANSCEIVER COMPRISING: LOGIC MEANS FOR GENERATINGPERIODIC TIMING PULSE PATTERMS, TIMING MEANS RESPONSIVE TO SELECTED ONESOF SAID TIMING PULSE PATTERNS FOR GENERATING A PLURALITY OF REPETITIVETIMING SIGNALS IN PHASE WITH SAID TIMING PULSES, SELECTIVELY ENERGIZABLEFACSIMILE TRANSMITTER SCANNING MEANS RESPONSIVE TO SAID TIMING MEANS FORGENERATING VIDEO SIGNALS CORRESPONDING TO THE INFORMATION CONTENT OF ANORIGINAL DOCUMENT TO BE TRANSMITTED, SELECTIVELY ENERGIZABLE FACSIMILERECEIVER PRINTER MEANS RESPONSIVE TO RECEIVED SIGNALS FOR GENERATING AFACSIMILE CORRESPONDING TO RECEIVED VIDEO SIGNALS, FIRST CONTROL MEANSRESPONSIVE TO THE DETECTED PRESENCE OF A DOCUMENT TO BE TRANSMITTED FORENERGIZING SAID TRANSMITTER SCANNING MEANS, AND, SECOND CONTROL MEANSRESPONSIVE TO THE DETECTED ABSENCE OF AN ORIGINAL DOCUMENT TO BETRANSMITTED AND TO RECEIVED VIDEO SIGNAL FOR ENERGIZING SAID FACSIMILERECEIVER PRINTER MEANS.